Calcium- and phorbol ester-dependent calponin phosphorylation in
homogenates of swine carotid artery.
Rokolya, Anik[acute]o, Michael P. Walsh, and Robert S. Moreland.
Bockus Research Institute, Graduate Hospital, Philadelphia, PA
19146 USA, and Department of Medical Biochemistry, Faculty of
Medicine, University of Calgary, Calgary, Alberta, T2N 4N1 Canada
APStracts 3:0088H, 1996.
Calponin inhibits actin-activated myosin ATPase activity and
phosphorylation reverses this inhibition. Calponin phosphorylation
has been demonstrated in reconstituted contractile protein systems
but studies using intact smooth muscle have produced mixed results.
The goal of this study was to determine if vascular smooth muscle
contains the necessary biochemical machinery to catalyze calponin
phosphorylation. We used swine carotid homogenate which allows access
to the intracellular components and contains all endogenous proteins
and enzymes in physiologically relevant concentrations. We
demonstrated that calponin is phosphorylated in response to Ca2+
(0.27 +/- 0.04 mol Pi/mol calponin) and in response to phorbol
dibutyrate in the presence or absence of Ca2+ (0.48 +/- 0.09 mol
Pi/mol calponin). Calponin phosphorylation was inhibited by the
protein kinase C inhibitor, staurosporine but not by the Ca2+- and
calmodulin-dependent protein kinase II inhibitor, KN-62. We conclude
that Ca2+-dependent and -independent isoforms of protein kinase C but
not the calcium and calmodulin dependent protein kinase II catalyze
calponin phosphorylation in the swine carotid artery.
Received 14 August 1995; accepted in final form 6 February 1996.
APS Manuscript Number H768-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96